1. Field of the Invention
The present invention relates to specialized sheet metal cutting tools and, more particularly, relates to a tool having a point configuration and design uniquely suited to removal of spotwelds which join two or more layers of sheet metal, thereby freeing the sheet metal layers from one another.
2. State of the Prior Art
A construction technique frequently used in the automobile industry and other industries involves joining prefabricated sheet metal parts together using a series of spotwelds which are spaced along the mating edges of the prefabricated sheet metal parts. This is particularly common among modern automobile manufacturers who often join structural elements and body parts together by using hundreds of spotwelds.
Occasionally it becomes necessary in automobile and other applications to separate such spotwelded parts. This most commonly occurs when one of the parts has been damaged such as when an exterior fender panel or door panel of an automobile has been damaged as a result of an accident. In such circumstances, it becomes necessary to remove the damaged piece quickly and easily and with minimum damage to the remaining structure so that a replacement piece can be welded in place.
One of the common prior art tools used for this task is an air powered chisel. The tip of such a chisel is forced between the mating surfaces of the sheet metal in the region of the spotweld and the lead edge of the chisel is aimed toward the spotweld. When activated, the power chisel drives forward and literally rips the welded metal apart. This process has the shortcoming that it is quite loud and jarring to the operator. More importantly, this technique has a dangerous tendency to distort the piece of sheet metal that is left behind. This distortion may lead to problems because it may prevent the replacement piece of sheet metal from fitting properly to the remaining structure.
A second prior art technique involves the use of the tool shown in FIGS. 5A and 5B. The tool resembles a milling bit with an aperture in the middle of the bit. The aperture is approximately the correct size to accommodate a typical spotweld. The cutting region of the tool, therefore, is in the shape of an annulus which surrounds the spotweld. The tool of FIG. 5A and 5B sometimes is provided with either a spring-loaded awl or a conventional steel drillbit in the center of the tool aperture to assist with centering. This tool has several shortcomings. When an awl is used, the tool is difficult to control. It tends to skate across the surface of the sheet metal, particularly when the tool is not perfectly perpendicular to the sheet metal surface. If a drillbit is used in the center of the tool, the drillbit helps to maintain the center and assists the operator by tending to pull the milling teeth into contact with the work surface. However, it also proceeds to drill through both pieces of sheet metal into whatever may be found behind the sheetmetal.
Equally important, the tool of FIGS. 5A and 5B leaves a series of small "discs" on the structure that are left behind after all of the spotwelds have been milled and the damaged piece of sheetmetal has been removed. These "discs" are left behind because the region of the tool with the cutting edges cuts a doughnut-shaped hole through one of the sheet metal layers. The spotweld location, however, remains partially or completely intact. Therefore, when using the tool of FIG. 5A and 5B, an additional operation is needed to prepare the remaining surface for a replacement part. This is frequently done with a grinder, which has at least two significant shortcomings. First, it is extremely noisy and messy. Second, a great deal of heat is generated in the vicinity of the spotweld by the grinding friction and this heat is rapidly conducted to the nearby sheetmetal. This can have the effect of deteriorating the metallurgical properties of the sheet metal in that region. It also can have the negative effect of melting and releasing rustproofing materials attached to the metal in that area.